The invention relates generally to mass spectrometry and more specifically concerns improvements in time-multiplexed mass spectrometry.
In chopped molecular beam mass spectrometry systems there is often a need to make several near-simultaneous measurements. This can be accomplished by time multiplexing. That is, several measurements are made and each measurement is sampled in a different assigned time interval within a time frame. The time frames are repeated many times. Hence, if the repeated time frames are displayed on an oscilliscope the averages of the different time intervals can be viewed. However, when a chopped molecular beam measuring system is time multiplexed there are several requirements of the combined system: The multiplexing must be synchronized with the chopper of the measuring system such that there is one transition of the chopper (a change from blocking the molecular beam to not blocking the molecular beam by the chopper) during each time interval. Otherwise, the measurements during each time interval of the multiplexing would not be capable of digital averaging over many repetitions of a time frame. There must be a capability for phase shifting the chopper with respect to the time intervals so that at a selected time during each multiplexing time interval there is a transition. Thus, a measurement of the effect of a transition can be made during each time interval at a selected time. The base lines of the measurements during the different time intervals should have the same reference level. That is, the measurements during all time intervals while the chopper is blocking the molecular beam should be the same. There should be the capability of independently varying the gain of each channel of the multiplexing system. There should be provided a means for blanking a measurement for a short period of time following the beginning of each time interval to allow for settling time.
It is therefore an object of this invention to time multiplex the measurements from a chopped beam measuring system.
Another object of this invention is to provide apparatus for time multiplexing the measurements from a chopped beam measuring system such that the measurements during each time interval are capable of digital averaging over many repetitions of a time frame.
A further object of this invention is to time multiplex the measurements from a chopped beam measuring system and synchronize the transitions made by the chopper with the time multiplexing time intervals.
Still another object of this invention is to time multiplex the measurements from a chopped beam measuring system, synchronize the transitions made by the chopper with the time multiplexing time intervals and provide means for phase shifting the transitions with respect to the time intervals.
A still further object of this invention is to time multiplex the measurements from a chopped beam measuring system and provide means for independently changing the reference level of the baseline in each time interval in a multiplexing time frame.
Yet another object of this invention is to time multiplex the measurements from a chopped beam measuring system and provide means for independently varying the amplitudes of the measurements in each time interval in a multiplexing time frame.
Yet still another object of this invention is to time multiplex the measurements from a chopped beam measuring system and provide means for blanking the measurements for a short period of time following the beginning of each time interval to allow for settling time.
Other objects and advantages of this invention will become apparent hereinafter in the specification and drawings.